# 14) Swap(lat, lon) by ID parity check
UPDATE citytable
	SET lat = lat + lon, lon = lat-lon, lat = lat - lon
	WHERE CASE WHEN 'od' = 'ev' THEN id % 2 = 0
			   ELSE id % 2 = 1 END;
    
# 15) SET lat = lon where ones place of ID is m
UPDATE citytable
	SET lat = lon
	WHERE id % 10 = 6;

# 16) Query kth symmetric pair
#Format : kth = LIMIT k-1, 1
SELECT f1.X, f1.Y
	FROM (SELECT ROUND(lat, 1) X, ROUND(lon, 1) Y
		FROM citytable) f1
			INNER JOIN 
		 (SELECT ROUND(lat, 1) X, ROUND(lon, 1) Y
		FROM citytable) f2 
			ON f1.X=f2.Y AND f1.Y=f2.X
	GROUP BY f1.X, f1.Y
	HAVING COUNT(f1.X) > 1 or f1.X < f1.Y
	ORDER BY f1.X, f1.Y LIMIT 1, 1;